1. Field of the Invention
The preparation of 2-alkylidene ketones and aldehydes by direct aldol condensation of an aldehyde with a ketone is usually not a practical synthetic method. Because of the value to the manufacturer of perfume intermediates, a considerable amount of research has been carried out to develop better methods of preparing the above-mentioned novel 2-alkylidene ketones and 2-alkylidene aldehydes.
2. Description of the Prior Art
In the prior art, Seebach et. al., Tetrahedron Letters, 3171-3174 (1974), describes a process for transforming ketones and aldehydes into .alpha.,.beta.-unsaturated ketones using silylated dithiane anions and ketones.
Also in the prior art, Smith et al., J. Org. Chem., 35, 3220-3223 (1970), teach the reaction of boron difluoride complexes of 2-formylketones with organometallic reagents as constituting an effective synthesis of 2-alkylidene ketones.
Another prior art reference, Ansell et al., J. Chem. Soc., 329-331 (1959), teaches the reaction of 2-isobutoxycyclopent-2-enone with isobutyl alcohol in the presence of toluene-p-sulfonic acid to yield 2-substituted cyclopent-2-enones.
Still another prior art reference is Japanese Patent No. 51-23240 (Feb. 24, 1976), which reference claims the manufacture of 2-alkyl-2-cyclopentenone by contact of 2-alkyldienecyclopentanone with hydrogen halide or sulfonic acid.
Yet another prior art reference is Martin et al., Tetrahedron Letters, 4459-4462 (1976), which reports an allegedly facile, new procedure for the efficient preparation of a number of .alpha.-alkylidene-.gamma.-butyrolactones starting from .gamma.-butyrolactones and proceeding via .alpha.-n-butylthiomethylene-.gamma.-lactones which are allowed to react with lithium dimethylcuprate or lithium di-n-butylcuprate to yield corresponding .alpha.-alkylidene-.gamma.-lactones.
Still another reference is that of Katsin et. al., Synthetic Communications, 7 (3) 185-188 (1977), which describes a synthesis of 2-alkylcyclopent-2-en-1-ones and the corresponding cyclopentanones.
The reaction of dimethylformamide diethyl acetal with acetophenone or acetone is disclosed in Bredereck et al., Ber. 97, 3397-3406 (1964).